CN1213418C - Optical head for scanning record carrier - Google Patents

Optical head for scanning record carrier Download PDF

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Publication number
CN1213418C
CN1213418C CNB018061230A CN01806123A CN1213418C CN 1213418 C CN1213418 C CN 1213418C CN B018061230 A CNB018061230 A CN B018061230A CN 01806123 A CN01806123 A CN 01806123A CN 1213418 C CN1213418 C CN 1213418C
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China
Prior art keywords
beamlet
laser beam
radiation
center
radiation laser
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CNB018061230A
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Chinese (zh)
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CN1411598A (en
Inventor
J·E·德弗里斯
B·H·W·亨德里克斯
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Koninklijke Philips NV
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Koninklijke Philips Electronics NV
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B7/1374—Objective lenses
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/10532—Heads
    • G11B11/10541—Heads for reproducing
    • G11B11/10543—Heads for reproducing using optical beam of radiation
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only
    • G11B7/0912—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only by push-pull method
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
    • G11B7/127—Lasers; Multiple laser arrays
    • G11B7/1275—Two or more lasers having different wavelengths
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1353—Diffractive elements, e.g. holograms or gratings
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/139—Numerical aperture control means
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1392—Means for controlling the beam wavefront, e.g. for correction of aberration
    • G11B7/13922—Means for controlling the beam wavefront, e.g. for correction of aberration passive
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
    • G11B2007/0006—Recording, reproducing or erasing systems characterised by the structure or type of the carrier adapted for scanning different types of carrier, e.g. CD & DVD

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Head (AREA)

Abstract

A device for scanning a first and second type of optical record carriers (2; 40) of different thickness generates a first and a second radiation beam of different wavelengths. The first radiation beam (17) has a first numerical aperture NA1. The second radiation beam (46) has an effective second numerical aperture NA2 smaller NA1. The rays of the second radiation beam having an NA smaller than NA2 form a central sub-beam (48), the rays having a larger NA form an outer sub-beam (49). The device includes a non-periodic phase structure that does not affect the first radiation beam. The introduced spherical aberration compensates the difference in spherical aberration caused by the difference in thickness of the transparent layers (3; 41). To reduce the amount of stray light falling on the detection system (25) from rays in the outer sub-beam (49), the phase structure introduces an amount of defocus in the second radiation beam (17). Which displaces the focus of the central sub-beam with respect to of the outer sub-beam, causing the intensity distribution of the central and outer sub-beam to split in two separate distributions. If the position and size of the detection system are properly chosen, the detection system will capture mainly rays from the central sub-beam and not from the outer sub-beam. Hence, the displacement of the foci allows spatial filtering in the plane of the detection system (25) of the desired and undesired rays of the second radiation beam.

Description

The shaven head that is used for scanning record carrier
Technical field
The present invention relates to a kind of shaven head that is used to scan the first and second dissimilar record carriers.The invention still further relates to a kind of device that is used to scan two dissimilar optical record carriers, described device comprises shaven head.Two types record carrier has Information Level and hyaline layer, can the scanning information layer by the hyaline layer radiation beam.For two types record carrier, transparent layer thickness is different.Shaven head comprises radiation source, is used to produce the radiation beam of record carrier that is used to scan the first kind with first wavelength, with second radiation beam of record carrier that is used to scan second type with second different wavelength.First radiation beam has bigger effective numerical aperture than second radiation beam, is used for the scanning information layer.
Background technology
Progress in the optical recording field makes and has occurred the new optical record carrier that has than high information density on the market.In general, designing these record carrier utilizations wavelength different with the record carrier before the scanning and the radiation laser beam of numerical aperture scans.Need be designed for the record carrier that the scanister of new record carrier can scan both old.Therefore, scanister must be revised like this, makes it that two class radiation laser beams can be provided, and every class record carrier is with a kind of.The performance of radiation laser beam depends on the characteristic of record carrier.The wavelength of radiation laser beam depends on the wavelength dependence of optical property of mark of the record carrier of recorded information.Determine the wavelength of radiation laser beam of the resolution that can be used for scanning and the size that numerical aperture depends on mark.The quantity of the spherical aberration compensation of radiation laser beam depends on the thickness of the hyaline layer of record carrier, and radiation laser beam is by described hyaline layer scanning information layer.For example, the device of record carrier that is applicable to the so-called DVD type of scanning provide have the 660nm wavelength, 0.6 numerical aperture (NA) and the substrate thickness that is used for record carrier be first radiation laser beam of the spherical aberration compensation of 0.6mm.For the record carrier of the CD type that writes previous generation, described device also provides second radiation laser beam, and its wavelength is 785nm, and 0.50 NA and record carrier substrate thickness are the spherical aberration compensation of 1.2mm.Described device preferably has one and is used for radiation laser beam is focused on objective system on the record carrier, so that keep low manufacturing cost.The change of numerical aperture realizes by the diameter that the radiation laser beam on the objective system is incided in change.
Article " Dual-Wavelength optical head with a wavelength-selective filter for 0.6-and 1.2-mm-thick-substrate opticaldisks " (people such as Katayama, Applied Optics, Vol.38, No.17, p 3778-3786, on June 10th, 1999) disclosed a kind of shaven head, it has an objective system, is used for scanning the device of DVD and two types of records of CD.Radiation source produces first and second radiation laser beams, is respectively applied for scanning DVD and CD record.An optical system focuses on radiation laser beam on the Information Level of record carrier.Optical system comprises an optical element, and it is the form of the plane-parallel plate with non-periodic phase structure.The diameter of first and second radiation laser beams is equal substantially in the plane of described optical element.Second radiation laser beam can be thought and comprises a center beamlet and an outside beamlet.First radiation laser beam focuses on the record carrier of DVD type with 0.6 first numerical aperture, and the center beamlet focuses on the record carrier of CD type with 0.45 second value aperture.Described phase structure comprises a plurality of concentric zones, and they form a light path figure, is used for introducing a wavefront skew by the radiation laser beam of described phase structure.Phase structure has the diameter corresponding to the center beamlet, and causes spherical aberration in the beamlet of center, is used to compensate the thickness difference of hyaline layer.Make the path difference between the zone equal the integral multiple of first wavelength in the difference in height between the adjacent area, make phase structure invalid thus for first radiation laser beam.Optical element around the phase structure is provided with the film interference duplexer.Design the folded body of described interfering layer and be used for seeing through the first radiation laser beam Z, and cut off outside beamlet.Like this, described optical element sees through first radiation laser beam, and do not influence its wavelength, and has a diameter corresponding to the first bigger numerical aperture, it sees through the center beamlet, introduces spherical aberration, and has the diameter corresponding to less second value aperture, and it cuts off outside beamlet, promptly is arranged in the light of second radiation laser beam of the outside of central light beam.
The shortcoming of this known shaven head is, owing to the existence of phase structure and thin-film laminate causes the element cost quite high.In addition, described thin-film laminate complexity because it must introduce predetermined phase deviation in first radiation laser beam, so as to realize seeing through duplexer radiation laser beam part wavefront and see through the part same-phase of phase structure.
Summary of the invention
The object of the present invention is to provide a kind of shaven head that comprises cheap optical element with phase structure.
The objective of the invention is to realize by a kind of shaven head, described shaven head is used to scan first optical record carrier that comprises first information layer and first hyaline layer with first thickness and comprises second optical record carrier of second Information Level with second hyaline layer with second thickness different with first thickness, described shaven head comprises radiation source, be used to produce first radiation laser beam with first wavelength, with second radiation laser beam with second wavelength different with first wavelength, described second radiation laser beam comprises a center beamlet and outside beamlet, an optical system, be used to assemble first radiation laser beam and focus on first information layer by first hyaline layer, and assemble second radiation laser beam and focus on second Information Level by second hyaline layer, and detection system, be used to receive radiation from first and second radiation laser beams of Information Level, and comprise the photosensitive region that is arranged in the detection plane, described optical system comprises the optical element with non-periodic phase structure, described phase structure comprises a plurality of concentric regions, be used for causing a wavefront skew that is offset near a flat wavefront on the whole at first radiation laser beam, and in the beamlet of center, cause the wavefront skew of the difference of the spherical aberration that a compensation causes owing to the different-thickness of first and second hyaline layers, wherein, according to the present invention, described optical element is transparent for the center beamlet and the outside beamlet of first radiation laser beam and second radiation laser beam, and the wavefront that produces in second radiation laser beam skew is such, when the focus of central center light beam is positioned on second Information Level, the radiation of center beamlet and outside beamlet forms center intensity distribution and external intensity respectively and distributes in detection plane, described center intensity distributes and external intensity distributes by a basic dark zone separately, and described photosensitive region is only caught the radiation that described center intensity distributes basically.
Need not to have thin-film laminate as the outside beamlet of blocking-up that has according to optical element of the present invention in known shaven head, it is transparent for the radiation of first and second wavelength on the whole diameter of first and second radiation laser beams basically.Because in according to shaven head of the present invention, do not need thin-film laminate, comprise the low cost of manufacture of the optical element of phase structure.In addition, do not have thin-film laminate to make and realize that in the whole diameter range of first radiation laser beam flat wavefront becomes simply, because can keep the correct phase place of first radiation laser beam by the thickness of in the whole diameter range of first radiation laser beam, reasonably selecting the zone of phase structure.Described optical element can be any element of supporting in the optical system of described phase structure, for example plane-parallel plate, beam splitter or lens.
Described phase structure is proofreaied and correct the center beamlet, so that eliminate the poor of spherical aberration, produce the measured luminous point of matter on second Information Level, and the center intensity that produces in detection plane quite among a small circle distributes.There is not the thin-film laminate can be so that arrive record carrier in the radiation of second radiation laser beam of the first numerical aperture outside.Because outside beamlet does not carry out the correction for the spherical aberration of eliminating second hyaline layer, because the deviation of the thickness of second hyaline layer and will present sizable aberration.The ray of outside beamlet will arrive detection plane, and they will form the radiation profiles of its scope greater than the center intensity distribution range in described detection plane.When two kinds of radiation profiles superpose in detector plane, the radiation of center beamlet and outside beamlet will be incided on the photosensitive region of detection system.In this case, be difficult between the ray of the ray of center beamlet and outside beamlet, promptly discern having less than the radiation of the numerical aperture in second value aperture and have between the radiation of bigger numerical aperture.If detection system is caught the ray with bigger numerical aperture, cause that then utilization scans second record carrier greater than the numerical aperture in required second value aperture.Because cube broom shape wavefront error that is directly proportional of one of the inclination of record carrier introducing and numerical aperture, the increase of scanning numerical aperture will reduce the tolerance in the record carrier inclination.In addition, the ray from outside beamlet may increase by the noise in the electric signal of detection system generation.
If correctly selected by the wavefront skew that phase structure produces in second radiation laser beam, then outside beamlet will form one and the overlapping radiation profiles of the central distribution of getting along well.This so-called external intensity distributes and distributes separately by a dark basically zone and center intensity.Separation between two distributions allows the ray in second radiation laser beam is carried out spatial filtering, and this is by the photosensitive region of detection system is set like this, makes the light of its main trap center intensity distributions realize.This record carrier will scan with required numerical aperture then.Thereby, use quite cheap optical element with non-periodic phase structure, can keep external intensity to distribute effectively away from detection system.
" mainly " speech means that approximately the intensity that distributes less than 30% external intensity falls on the photosensitive region, preferably less than 10%.
Before detection system, the light of outside beamlet can utilize a film to be blocked, thereby stops them to fall on the radiation sensitive regions of detection system.But, the edge of radiation sensitive regions is preferably disposed in the dark areas of intensity distributions, implementation space filtering thus.Detection system can be arranged in the center intensity distribution, and its position and size are not required accurate tolerance.
Center intensity distributes and the separating and can realize by the appropriate combination in the first and second transparent layer thickness differences and second value aperture of external intensity distribution.When the thickness of second hyaline layer during greater than the thickness of first hyaline layer, the focus of outside beamlet is not eliminated the spherical aberration that produces owing to thickness difference through overcorrect, its position change by second Information Level is position, an objective system further away from each other on the objective lens system optical axis.In other words, compare with the paraxial focus of second light beam, the marginal focus of second light beam is further removed from objective system.In the middle of the focus of center light beam when being positioned on second Information Level of record carrier of second class, the radiation of this beamlet forms the center intensity distribution in detection plane.The focus of outside beamlet moves vertically with respect to the focus of center beamlet, makes the radiation of beamlet be positioned at outside the focus of detection plane, therefore forms to have the annular, outer intensity distributions concentric with the central area in detection plane.If defocus amount is correct, then central distribution and outside distribution will be separated by dark areas, thereby can carry out spatial filtering.
In a particular embodiment, in second radiation laser beam, introduce spherical aberration and defocusing, the axial distance between the described focus that defocuses the focus that influences the center beamlet and outside beamlet according to phase structure of the present invention.
In a certain embodiments, phase structure is introduced in the beamlet of center and is defocused.The scope of phase structure can be defined in the xsect of the center beamlet in the optical element plane.The focus servosystem of shaven head will make the focus of center beamlet be positioned at the plane of second Information Level, and the focus of outside beamlet compare with described plane be positioned near or away from the position of object lens.
In another embodiment, phase structure is externally introduced in the beamlet and is defocused.At this moment, phase structure will extend in the whole diameter range of second radiation laser beam.Externally under the situation that the focus of beamlet moves along the direction of objective system, do not defocus if do not introduce in the part of the phase structure of introducing spherical aberration, the complicacy that then is used to introduce the phase structure of spherical aberration can be reduced.
Make the influence minimum of phase structure to first radiation laser beam, if promptly, preferably, the difference between the light path of the adjacent area of phase structure is substantially equal to the integral multiple of first wavelength, and then phase structure is introduced a wavefront skew that integral body is flat.
Preferably, defocus amount is 12.5 microns at least, so that a rational dark areas of size is arranged.
Another aspect of the present invention relates to a kind of device that is used to scan two class optical record carriers, and described device comprises above-mentioned shaven head and is used for the information process unit of error correction.When scanning during the second class record carrier, the minimizing of the amount of stray light on the detecting device makes the noise the electrical information signal that produced by detection system and the information that representative is read from described record carrier reduce.Phase structure also increases the inclination limit of second record carrier, reduces the coma aberration quantity in radiation laser beam thus, and cross (talk) between the relevant track and the interference between the internal symbol.The better quality of information signal makes the wrong number in the signal reduce, and reduces the requirement that is used for error correction that is added on the information process unit thus.
Description of drawings
Purpose of the present invention, advantage and feature are below to will be more obvious in the more specific description of the preferred embodiments of the present invention shown in the drawings, wherein:
Fig. 1 represents according to scanister of the present invention;
Fig. 2 represents to have the optical element of conventional phase structure;
Fig. 3 A and Fig. 3 B represent to be used for the radiation profiles in the detection system plane of conventional phase structure and phase structure of the present invention respectively;
Fig. 4 represents the schematic section of the light path of scanister;
Fig. 5 represents to have the quad detectors of intensity distributions;
Fig. 6 represents the sectional view of optical element and for two different wave length λ 1And λ 2Path difference; And
Fig. 7 is the figure identical with Fig. 6, and expression is used for having at phase structure the optical element of tilting zone.
Embodiment
Fig. 1 represents to be used to scan the device 1 of second record carrier 40 of first optical record carrier 2 of the first kind and second type.In an illustrated embodiment, the first kind is digital versatile disc (DVD), and second type is the CD (CD) that can write.Record carrier 2 comprises hyaline layer 3, and the one side is provided with Information Level 4.A side that deviates from hyaline layer of Information Level is protected from the influence of environment by protective seam 5.One side of hyaline layer facing device is called as input face 6.Hyaline layer 3 is used for providing mechanical support to Information Level as the substrate of record carrier.As selection, hyaline layer also has the substrate function of protection Information Level, provides mechanical support by the layer on the opposite side of Information Level to Information Level simultaneously, for example by protective seam 5 or by another Information Level and the hyaline layer that link to each other with Information Level 4.Information can be stored on the Information Level 4 of record carrier, and described record carrier is the form of the detectable mark of light, and the basic upper edge of described mark is parallel, and concentric or spiral track setting does not illustrate among the figure.Mark can be taked the readable form of any light, for example with the hole form, perhaps be have reflection coefficient or with its around different direction of magnetization forms, the perhaps combination of these forms.
Scanister 1 comprises radiation source, and it can launch the radiation laser beam 7 and 8 of first and second different wave lengths.Radiation source shown in the figure comprises two semiconductor lasers 9 and 10, their emitted radiation light beams 7 and 8.Beam combiner 11, for example translucent sheet synthesizes a light path to the light path of two light beams 7 and 8.Two radiation sources can be combined on the substrate, and if two radiation sources enough approaching, beam combiner 11 can save.First radiation laser beam is used to scan the record carrier 2 of the first kind.Second radiation laser beam 8 is used to scan the record carrier 40 of second type.From the radiation laser beam of dispersing 12 of beam combiner 11, described lens are converged to collimated light beam 15 to the light beam of dispersing 12 to second beam splitter 13 in reflection on the light path of collimation lens 14.Collimated light beam 15 incides on the transparent optical element 16, and it changes the wavefront of collimated light beam.Light beam 17 from optical element 16 incides on the objective system 18.Described objective system can comprise one or several lens and/or grating.Transparent optical element 16 can be integrated in the objective system 18.Objective system 18 has optical axis 19.Objective system 18 becomes convergent beam 20 to light beam 17, incides on the incidence surface 6 of record carrier 2.Objective system has and is used to make the spherical aberration correction of first radiation laser beam by the thickness of hyaline layer 3.Convergent beam 20 forms luminous point 21 on the Information Level 4 of first record carrier 2.Form divergent beams 22 by Information Level 4 radiation reflected, it is converted to the light beam 23 of collimation basically by objective system 18, converts convergent beam 24 to by collimation lens 14 subsequently.Beam splitter 13 splits into light beam and folded light beam forward by at least a portion towards detection system 25 transmission convergent beams 24.Detection system has the radiation sensitive regions that is arranged in detection plane 25 '.The radiation sensitive regions of detection system is caught described radiation laser beam, and converts thereof into electrical output signal 26.Signal processor 27 converts these output signals to various other signals.One of them signal is an information signal 28, the information that its value representation is read from Information Level 4.Information signal is handled by information process unit, carries out error correction 29.Other signal from signal processor 27 is focus error signal and radial error signal 30.Focus error signal is represented the axial difference along short transverse between luminous point 21 and the Information Level 4.Radial error signal represent luminous point 21 and the Information Level of following by described luminous point in the center of track between distance in the plane of Information Level 4.Focus error signal and radial error signal are sent into servo-drive system 31, and its these conversion of signals become servo-control signal 32, are used for controlling respectively focus actuator and radial actuator.Described actuator does not illustrate in the drawings.Focus actuator is controlled the physical location of luminous point 21 thus along the position of focus direction 33 control objective systems 18, makes it consistent with the plane of Information Level 4 basically.Radial actuator is the position of 34 control object lens 18 radially, so as to the radial position of control luminous point 21, makes it consistent with the center line of tracked track in the Information Level 4 basically.Described track edge in the drawings extends perpendicular to the direction on the plane of figure.
The device of Fig. 1 is made amendment according to the present invention and is made second record carrier 40 also be used to scan second type.This record carrier comprises thicker hyaline layer 41, Information Level 42, protective seam 43 and the plane of incidence 44 of a ratio first record carrier 2.Described device uses second radiation laser beam, 8 scanning information planes 42.The numerical aperture of second radiation laser beam (NA) can be suitable for obtaining convergent beam 45, and it has the NA of the focus 47 that is suitable for being formed for scanning information layer 42.The suitable value of NA is the NA of first numerical aperture 0.6 for DVD type record carrier 1, be the NA in second value aperture 0.5 for the CD type record carrier that can write 2In general, second radiation laser beam 46 is bigger than being used to form the required diameter of convergent beam 45.The part that forms second radiation laser beam 46 of convergent beam 45 is called center beamlet 48, and the annular section that centers on second radiation laser beam of center beamlet 48 is called outside beamlet 49.
The spherical aberration compensation of objective system 18 is not suitable for the thickness of hyaline layer 41, and this is because due to the different wavelength of described hyaline layer and the different thickness.Design optical element 16 is used to introduce the wavefront skew, and when second radiation laser beam passed through described optical element, described wavefront skew had the form of spherical aberration.The spherical aberration of introducing in the center beamlet 48 in inciding objective system is selected like this, makes the spherical aberration that the spherical aberration compensation of the combination introduced in radiation laser beam by optical element 16 and objective system 18 is produced during by hyaline layer 41 by radiation laser beam.
Fig. 2 represents the example by the xsect of the optical axis 19 of optical element 16.Optical element comprises transparent panel 50, and one surface 51 has phase structure 52, and described phase structure is the rotation symmetry around optical axis 19.Phase structure shown in the figure has central area 53 and 8 concentric annular region 54-61.These zones have different height, thereby form the different light path of the light of the radiation laser beam that passes through the optical element transmission.These regional height have been exaggerated with respect to the thickness and the radial extension of plate 50 among the figure.As described below, the correct design of phase structure makes it possible to have wavelength X 1And λ 2First and second radiation laser beams in introduce a predetermined wavefront skew respectively.In the embodiment of device shown in Figure 1, phase structure is not introduced the wavefront skew in first radiation laser beam, in the beamlet of the center of second radiation laser beam, introduce spherical aberration and may introduce defocusing, and in the outside beamlet of second radiation laser beam, do not introduce the wavefront skew.
If incorrect by the wavefront skew selection that phase structure is introduced, then the intensity distributions in the plane of detection system will have the form of the distribution 70 shown in Fig. 3 A.This center of being distributed in has the highest intensity, reduces along with leaving the center.Dotted circle 71 is such annulus, has less than NA 2The light of numerical aperture, promptly from center beamlet 48 and should be positioned at its inside by the light that detection system is caught.From the light portion of outside beamlet 49 drop on the inside of annulus, partly drop on the outside of annulus, and in the electric signal that produces by detection system, cause noise, and reduce the franchise of device.A detection system is set, makes that its light of catching from center beamlet 48 is difficult.
Fig. 3 B represents the radiation profiles 70 ' in the plane of the detection system 25 of second radiation laser beam when using the phase structure of correct design.In the plane of detection system, the external intensity distribution 73 of center intensity distribution 72 and annular can be distinguished, be separated by annular dark areas 74.From having of center beamlet less than NA 2The light of numerical aperture be limited in the central distribution 72.The light that distributes from the outside with bigger numerical aperture drops in the outside distribution 74.Provide the correct separation of two kinds of distributions according to phase structure of the present invention, thus make need and and unwanted light can realize that accurate space isolates.The physical size that Crape ring makes detection system can relatively be independent of the radiation sensitive regions of detection system is correctly located.This make again the focus of the center beamlet on Information Level 42 and outside beamlet the focal position move axially the generation that helps dark areas.
Between the focus of the focus of center beamlet and outside beamlet, introduce the effect of focus bias below with reference to Fig. 4 explanation.Collimation lens 14 is by line 80 expressions, and objective system 18 is by line 81 expressions, and Information Level 42 is by line 82 expressions, and detection plane 25 ' is by line 83 expressions.The scope of the radiation sensitive regions of detection system is by thick line 84 expressions.Optical axis is by dotted line 85 expressions.Shown in this figure is that optical element is integrated in the situation in the object lens.First's supposition of this explanation, record carrier 40 is not used in the hyaline layer 41 to Information Level 42 transmitted radiation light beams.Be suitable for less than NA 2The light 86 of radius of radiation laser beam of NA focus on the Information Level on the optical axis 85 82 by lens 81.After reflection, light is calibrated by object lens 81, and is assembled by collimation lens 80, thereby passes through detection plane 83 on optical axis.Light 87 is being suitable for greater than NA 2The radius of radiation laser beam of NA in, and before inciding objective system, with light 86 parallel advancing.The defocus amount that objective system produces is for having NA＜NA 2The center beamlet in light and have NA＞NA 2Outside beamlet in the light difference.The example of Fig. 4 represents that objective system is compared to the center beamlet for outside beamlet and has bigger focal length.If the center beamlet defocus distance between increment mirror system and the center beamlet focus, then the distance, delta z between two focuses is taken as negative.The value of Δ z is born among the figure.
Light 87 should be at the intersection point one segment distance Δ z place and the optical axis intersection of leave message layer 82 and optical axis.But, the reflection on Information Level is guided light into objective system 81 again.Objective system 81 and collimation lens 80 make back and the optical axis intersection of light in detection plane 83.As long as the scope of radiation sensitive regions 84 is enough little, light just can not blocked by described zone.Learn that by paraxonic calculating the light with numerical aperture NA 87 on Information Level 82 intersects at height r that is provided by following formula and detection plane 83:
r ( NA ) = | 2 NA F servo F obj Δz | - - - ( 1 )
F wherein 0And F cIt is respectively the focal length of objective system and collimation lens.When
| Δz | > R d F obj 2 N A 2 F servo - - - ( 2 )
The time, then be suitable for greater than NA 2The light of NA do not drop on and have radius R dRadiation sensitive regions 84 on.Work as R d=50 microns, F Obj=2.75 millimeters, F Servo=11 millimeters, NA 2=0.5 o'clock, the absolute value of Δ z | Δ z| must be greater than 12.5 microns.
When record carrier has the hyaline layer 3 of different-thickness and 41 the time, according to the type of record carrier, the spherical aberration of some will take place light.Because the spherical aberration that the thickness difference Δ d of hyaline layer causes is by W Disc(ρ) provide, ρ is by NA 2The pupil coordination of nominal is promptly corresponding to NA 2, ρ=1.In this example, the phase structure on optical element is for the center beamlet, promptly for having NA＜NA 2Light compensation W Disc(ρ), and for the center beamlet introduce defocusing that equals Δ z corresponding to the axial dipole field of focus.Not to outside beamlet compensation thickness difference Δ d, also moving focal point not.When having aberration, outside beamlet has its best focal position, and a distance, delta z is moved in the described focal position never position during aberration bIf the axial distance between the focus of the focus of center beamlet and outside beamlet satisfies
| Δz - Δ z b | > R d F obj 2 N A 2 F servo - - - ( 3 )
Then the light of outside beamlet will not incide on the sensitive surface 84.
When only considering three rank aberrations, can obtain Δ z bEstimation.Total wave front aberration W (ρ), the wave front aberration W that it is caused by thickness difference Δ d Disc(ρ) and the focal shift Δ z of the focus of outside beamlet bThe wave front aberration that causes constitutes, and is provided by following formula:
W(ρ)＝W disc(ρ)+W focus_out(ρ) (4)
Wherein
W disc ( ρ ) = - 1 8 Δd n 2 - 1 n 3 N A 2 4 ρ 4 - - - ( 5 )
W focus _ out ( ρ ) = 1 2 Δ z b N A 2 2 ρ 2 - - - ( 6 )
Wherein n is the refractive index of hyaline layer 41.Wave front aberration in formula (5) and formula (6) is represented as the polynomial form of Seidel.For NA＜NA 2And the W of wave front aberration DiscThe spherical aberration item that (ρ) is directly proportional is compensated by phase structure, is also produced the focal shift of Δ z simultaneously by phase structure.The desired positions of the focus of outside beamlet can be by making as defocusing position Δ z bThe minimum value of path difference (OPD) of outside beamlet of function try to achieve:
OP D 2 = 2 ∫ 1 ρ 1 W ( ρ ) 2 ρdρ ρ 1 2 - 1 - ( 2 ∫ 1 ρ 1 W ( ρ ) ρdρ ρ 1 2 - 1 ) 2 - - - ( 7 )
ρ wherein 1=NA 1/ NA 2For
Δ z b = 1 4 Δd n 2 - 1 n 3 NA 2 2 ( 1 + ρ 1 2 ) - - - ( 8 )
Obtain minimum value OPD.
For n=1.58, NA 2=0.5, ρ 1=1.2, Δ d=0.6mm, distance, delta z b=34.7 microns.The more accurate ray trace analysis of the optical system of Fig. 5 provides Δ z b=34.8 microns.If the position of outer focus is because the existence of spherical aberration and away from objective system, then Δ z bValue be positive.
Be applied to 12.5 microns minor increment between the focus that this routine formula (2) and (3) are created in the focus of center beamlet and outside beamlet.When the position grouping of the focus of itself and outside beamlet, i.e. Δ z bIn the time of=34.8 microns, for the light that makes outside beamlet does not drop on the sensitive surface of detection system, the amount of the defocus z that is introduced in the beamlet of center by phase structure must satisfy:
Δ z＜22.3 μ m or Δ z＞47.3 μ m.
In this specific example, when Δ z=0, obtain correct defocusing, phase structure was not introduced and was defocused this moment.The manufacturability that depends on optical element about the preferred value of Δ z.
If the concentric regions broad of phase structure, then optical element is made easily.If the slope of W (ρ) is less, then described regional broad.According to three rank aberrations, we find, when phase structure is introduced a defocus amount Δ z, must be provided by following formula by the wavefront W (ρ) of phase structure compensation:
W ( ρ ) = - 1 8 Δd n 2 - 1 n 3 N A 2 4 ρ 4 + 1 2 ΔzN A 2 2 ρ 2 - - - ( 9 )
When Δ z is provided by following formula:
Δz = 1 4 Δd n 2 - 1 n 3 N A 2 2 - - - ( 10 )
W (1)=0 then.The value of W hereto, wavefront is quite flat, this moment, phase structure was made easily.For above-mentioned example, this produces Δ z=14.2 micron.When W (1)＞0, the slope of wavefront diminishes, thereby further improves manufacturability, but makes the quality that reduces spatial filtering.In addition, when W (1)＜0, spatial filtering is enhanced, but the manufacturability variation.The preferred value of Δ z is to make wavefront have minimum maximum slope value.
In this embodiment, objective system 10 has lens, is used for wavelength X 1The parallel beam of the incident of=600nm focuses on the convergent beam that becomes NA=0.6, and it forms luminous point by hyaline layer 3 on Information Level.Free operating distance in this embodiment is 1.290mm.The thickness of hyaline layer is 0.6mm, is made by the polycarbonate of refractive index n=1.5803.The thickness of lens on optical axis is 1.922mm, and the diameter of entrance pupil is 3.3mm.Lens body is made by the SFL56 Schitt glass of refractive index n=1.7767.Radius towards the convex surface of the lens body of collimation lens is 2.32mm.Lens are spherical in shape, so that the spherical aberration that compensation is caused in first hyaline layer 3 by first radiation laser beam.Described sphere realizes by means of the propylene thin layer on Vitrea top.The refractive index n of paint film=1.5646.The thickness of this one deck on optical axis is 22 microns.Provide rotational symmetric sphere by following formula:
z(r)＝B 2ir 2i (11)
Wherein z is the surface location along the direction from the radiation source to the record carrier along optical axis, measures with millimeter, and r is the distance to optical axis, and unit is a millimeter, B kIt is the coefficient of the k time power of r.Coefficient B 2-B 14Be respectively 0.24134835,0.0051012159 ,-0.00098850422,0.00060334583 ,-0.00021740397,1.933136710 in this example -5With 1.658785510 -6
Optical element 16 is the non-periodic phase structure that 1.4891 flat PMMA plate is made by refractive index when 660 nanometers, and it is set at the side towards the object lens of collimation lens.Is 0h from optical axis 19 to high distribution of band with the radius of second value aperture coupling, 5h, 4h, 3h, 2h, 3h, 4h, 5h, 0h, wherein height h1=1.349 micron.The district the border respectively by 0.3322mm, 0.4893mm, 0.6241mm, 0.7728mm, 1.1537mm, 1.2413mm, 1.3010mm, 1.3497mm, 1.3900mm provides, they are respectively the last radiuses corresponding to the second value aperture.The focal length F of servo-lens SERVO=11mm.
Difference in height between the adjacent area equals the height h that provided by following formula 1M doubly:
h 1 = λ 1 n 1 - 1
λ wherein 1Be first wavelength, n1 is that the annular region material is in wavelength X 1Under refractive index.Multiple m can be any round values, for example-1,0 or 1.Concentric regions is 0,5 with respect to the height of central area 53,4,3,2,3, and 4,5 and 0 times h 1Adjacent area by phase structure is λ at the wavelength that passes optical element 1First radiation laser beam in the path difference (OPD) introduced equal mh 1(n 1-1), it equals m λ 1As a result, phase structure is introduced a flat wavefront skew to first radiation laser beam, and in other words, phase structure does not influence the wavefront of first radiation laser beam.
For the read/write operation of CD, wavelength X 2=780nm, NA=0.5.The refractive index of profiling layer under this wavelength of object lens is 1.5589, and the refractive index of the glass body of object lens is 1.7661, and the refractive index of PMMA plate is 1.4862, and the refractive index of polycarbonate transparent layer 41 is 1.5735.The thickness of hyaline layer 41 is 1.2mm.Free operating distance is 0.9550mm.In this case, the radius that meets the entrance pupil of NA=0.5 is 1.3900mm.
When second radiation laser beam passed through optical element 16, its wavefront was with influenced, and this is because it has and λ 1Different wavelength X 2, and the path difference of being introduced by concentric regions is not equal to λ 2Multiple.Now determine described path difference for specific phase structure shown in Figure 2.The material of concentric regions is polymethylmethacrylate (PMMA), for λ 1=660nm, refractive index n 1=1.4891 is for λ 2=785nm, refractive index n 2=1.4862.Table 1 expression is for bench height mh1, and wherein m has the value of 1-6, and path difference OPD is by λ 2The result who removes, i.e. (mh1 (n2-1) mod λ 2)/λ 2Notice that the height of the maximum in table provides minimum OPD.
Table 1
m {OPDmodλ 2}/λ 2
1 2 3 4 5 6 0.8411 0.6823 0.5234 0.3645 0.2057 0.0468
Selected height and a certain amount of spherical aberration of the feasible introducing of radial extension of annular region, it equals at wavelength is λ 2, NA 2Spherical aberration of introducing by the hyaline layer of 1.2mm in=0.5 the convergent beam 45 and the compensation in light beam 45, introduced by lens combination 18 with.Described with equal poor owing in the different spherical aberrations that produce of the thickness of the hyaline layer of record carrier.The sphere aberration of objective system, promptly at wavelength from λ 1Become λ 2The time, the order of magnitude of the difference of the spherical aberration that the order of magnitude of the change in the spherical aberration of being introduced by objective system produces less than the difference owing to thickness, and be believed to comprise in above-mentioned difference.According to the present invention, having increased quantity in the polynomial item of Zirnike is defocusing of 0.30 λ.The big distance of the positive symbolic representation that defocuses between central light beam and object lens.
Phase structure in the beamlet of center, introduce some be used to compensate the thickness difference between hyaline layer 3 and 41 and be used to compensate by object lens introduce since wavelength from λ 1Change into λ 2And the change of the spherical aberration that causes is the required spherical aberration of sphere aberration of object lens.What phase structure was also introduced some in the beamlet of center defocuses the focal shift Δ z corresponding to W (1)=0 that its generation equals 14.2 microns.
Calculate according to ray trace,, should obtain to have the best focal position of the light beam of NA＞0.5 when free operating distance during greater than 18.4 microns.Therefore, near the focus of the outside beamlet detection system is positioned at the back of detection plane, thereby forms the radiation profiles of annular in internal diameter is 80 microns detection plane.When use has radius R dDuring the detection system of=50 microns photosensitive region, this distribution makes it possible to carry out spatial filtering.When using this detecting device, the absolute value of the focal shift between interior outer light beam is more preferably greater than 11.3 microns.
In the above-mentioned example of phase structure, the best focal position of outside beamlet is 18.4 microns, than inner beamlet further from object lens, thereby allow to use 80 microns maximum detector radius.By at whole NA 1Extend aperiodic phase structure on the aperture, the focal shift between center beamlet and outside beamlet can further increase.If for NA＜NA 2Non-periodic phase structure and above-mentioned example in identical.Described non-periodic phase structure is at NA＞NA 2, or constitute by 3 steps in the scope of r＞1.39 millimeter.The scope of the concentric regions between these steps is 1.39-1.48mm, 1.48-1,57mm, 1.57-1.65mm.The height of these steps is respectively 2h1,1h1, and 0h1.The outside of non-periodic phase structure converts the outside beamlet of flat incident to be similar to convergent beam on the whole light beam.Object distance for the object lens of outside beamlet is changed into 1=-1260.4mm from negative infinity.This moment the focal shift Δ z of gained in image distance bProvide by following formula:
Δ z b = - F obj 2 l - - - ( 15 )
Obtain Δ z b=6.0 microns.As a result, when the free operating distance between object lens and dish increases by 18.4 microns+6.0 microns=24.4 microns with respect to the focus of center beamlet, obtain the best focal position of outside beamlet.The maximum detector increasing diameter that allows is added to 105 microns now.
Optical element with phase structure can utilize so-called duplication process manufacturing, deposit enamelled coating on substrate wherein, and Diacryl for example, by die forming with minus phase structure outline, and by the UV radiation hardening.As selection, optical element can utilize and in mould whole element be carried out injection molding and make, and half of described mould has the profile of phase structure.Optical element can also be operated with the reflection mode.In this case, the above-mentioned formula about h1 must be used h1=λ 1/ 2 replace, and table 1 also correspondingly changes.The wavefront of being introduced by the optical element of actual manufacturing can determine by the wavefront at the fore-and-aft survey radiation laser beam of optical element, and perhaps the height and the scope of the concentric regions by the Measurement Phase structure are determined.Under latter event, come match to comprise to defocus polynomial function with the spherical aberration item by the step-like wavefront that calculates by the size of phase structure.
Can utilize astigmatic method to make the embodiment of shaven head shown in Figure 1 be suitable for forming focus error signal 30.Described method is known.Provide lens 90 to shaven head, it is arranged in the light path of first and second radiation laser beams between beam splitter 13 and the detection system 25.Described lens are that 1.5734 polycarbonate is made by refractive index under second wavelength.Its thickness on optical axis is 0.9mm.A surface of lens is that radius is the cylinder of 15.5mm, and another surface is that radius is the sphere of 3.44mm.Lens 90 make the center beamlet form two focal lines, and one at the place ahead of detection plane 25 ' 0.299mm, and another is at the rear of detection plane 25 ' 0.355mm.When the focus of central center light beam was positioned on the Information Level 42, the so-called luminous point that is essentially annular of minimum scatter was in the detection plane, and had 55 microns geometric diameter D.This luminous point is that the center intensity of Fig. 3 B distributes 72.The focal line of astigmatism has length 2D.Fig. 5 is illustrated in distribute 91 position of center intensity on the radiation sensitive regions 92 of embodiment of detection system 25 of quad detectors form.Zone 92 is divided into 4 equal big subregions 93 by two lines 94.The axis of the cylinder of lens 90 becomes miter angle with the direction of line 94.As a result, the direction of focal line becomes miter angle with the limit of square detecting device, if square, the wavefront radiation sensitive regions should have the size of L * L, and wherein L approximates radical sign 2 greatly and multiply by D or bigger.In this embodiment of detection system, the size of regional 92L * L is 100 microns * 100 microns.The external intensity that there is shown in detection plane distributes 95.In order to prevent that the radiation that external intensity distributes from dropping on the radiation sensitive regions, the internal diameter that external intensity distributes should approximately be that radical sign 2 multiply by L or bigger.In the present embodiment, internal diameter should approximately be that radical sign 2 multiply by 100 microns=142 microns or bigger.The edge of radiation sensitive regions externally extends a bit of distance in the radiation profiles, as long as the radiation of the external radiation light beam that is interdicted is no more than above-mentioned quantity.Distance between the focus of the center beamlet that is formed by objective system and the focus of outside beamlet must be at least 16 microns, so that realize required internal diameter.The focal shift that calculates in focal shift and the foregoing description has the identical order of magnitude.
Can further improve spatial filtering by wavefront being carried out little correction.This can describe with reference to Fig. 6 and Fig. 7.The height h in the zone of the curve representation phase structure on the top of Fig. 6 is a unit with the function h1 as the phase structure radius.Note, the radius among Fig. 6 and Fig. 7 can out of true ground corresponding to the zone radius in the foregoing description.The phase structure of Fig. 6 does not comprise the feature of improved spatial filtering.Radius represents that according to the numerical aperture NA of the light in radiation laser beam described light is positioned at one section distance that equals described radius of central ray of leaving radiation laser beam.Provided by NA=r/f for the lens that meet so-called sine condition relation between radius r and the numerical aperture NA in air, f is the focal length of objective system 18.Showing respectively among the figure for CD and DVD is 0.5 and 0.6 NA.Perimeter 60 is positioned at zone 62, and it has 0 height and extends to NA 2With 0 zone 63 highly, it forms zone 61.In the curve 64 expression OPD at Fig. 6 middle part or the wavefront skew of being introduced in first radiation laser beam by phase structure, described OPD is the light path with respect to the central ray of light beam, with λ 1Be unit.The OPD of zone 54-60 bears, because light is postponed by phase structure shown in Figure 2.In other words, when the wavefront skew of introducing was convex, the shape of phase structure partly was spill.The dotted line 65 of portion is illustrated in the wavefront skew by introducing after the optical element transmission in first radiation laser beam in the drawings.Described wavefront skew is flat on the whole and partially, and the expression optical element does not influence first radiation laser beam.What objective system 18 was introduced somes is used for compensating the required spherical aberration of spherical aberration that the hyaline layer 3 at first kind record carrier is caused by first radiation laser beam.Thereby after by optical element 16 and objective system 18, first radiation laser beam is correctly compensated for first kind record carrier.
The curve 66 of wavefront skew bottom Fig. 6 of being introduced in second radiation laser beam by optical element illustrates.Along the OPD of Z-axis with λ 2For unit provides.Dashed curve 67-68 is the difference owing to the different spherical aberrations that cause of thickness of the hyaline layer of record carrier.The necessary quilt of described difference in spherical aberration is up to NA 216 compensation of=0.50 optical element are promptly up to the numerical aperture of second radiation laser beam of the record carrier that is used to scan second class.Bottom curve is represented, the approximate on the whole required spherical aberration 67 of step-like wavefront 66.But, described being similar to is being inappropriate on the value in concentric regions promptly on the local value: each zone provides a flat wavefront skew, and is not flat basically for the required wavefront skew in described zone.Difference on local value makes the correction imperfection of spherical aberration, as shown in the jaggies in the bottom diagram 69.This line is near the wavefront focus 47, with λ 2For unit is measured.Described wavefront is that the actual wavefront of the wavefront 67 that will be corrected and optical element is proofreaied and correct poor between 66.
Incomplete correct influences detection system 25 of second radiation laser beam detects the radiation laser beam that returns from record carrier 40.If the wavefront that sends with the light beam of directive detection system from optical element 16 is flat, then collimation lens 14 should correctly focus on the light that constitutes light beam on the intersection point of the central ray of radiation laser beam and detection system.The Wave-front phase error that spherical aberration causes though optical element has reduced in fact, it does not change the gradient or the gradient of wavefront.Because the local normal on wavefront is the radiation direction in the radiation laser beam, radiation direction can be tried to achieve by the normal of sawtooth profile 69.Wherein spherical aberration be corrected with profile 69 corresponding directions and the profile 67 that is not corrected of spherical aberration identical wherein.The direction of light is such: for less than about 0.35 NA, and light and more intersect near the central ray of the radiation laser beam of objective system 18 than having greater than the light of 0.35 NA.This makes the center and the external intensity of having widened in the detection plane distribute.
Fig. 7 shows the curve identical with Fig. 6, but phase structure wherein has the spatial filtering feature of improvement.The cross section of phase structure is shown in the curve at the top of Fig. 5.Described structure has on the plane of the upside of regional 54-57, and phase structure as shown in Figure 6 is such.Zone 58 ', 59 ' and 60 ' has oblique upside and replaces flat upside.Equally, zone 60 ' has oblique upside.The middle part curve representation of Fig. 7 is similar to the required flat wavefront of spherical aberration that causes when being used to compensate by first radiation laser beam by hyaline layer 3 on the whole for the wavefront 65 ' of first radiation laser beam.But, partly, described compensation is correct to regional 53-57 only, and wherein each zone forms flat basically wavefront.Described compensation shows as have little sawtooth in wavefront, as shown in the figure for zone 58 '-60 ' and 62 ' imperfection.This incomplete compensation reduces to 0.93 to the so-called Strehl intensity of luminous point 21 from 1.00, and this deterioration for the luminous point of scanning record carrier 2 is unconspicuous.
The curve representation of the bottom of Fig. 7 is for the OPD in the zone of second radiation laser beam.The compensation of zone 53-57 is incomplete, and this is similar with conventional phase structure.The upside that is chosen in the phase structure in the zone 58 '-61 ' tilts, and makes to form the local wavefront that equals the difference of spherical aberration 67, forms one thus near perfect compensation.This is illustrated by the flat wavefront 69 between NA=0.35 and NA=0.5 in the drawings.The zone 63 in for having greater than NA 1The not compensation of light of numerical aperture, thereby in the wavefront properties of spherical aberration, formed big gradient.In wavefront gradients, caused uncontinuity in transformation by zone 61 ' to 62 compensation, as in bottom diagram at NA 2Shown in the bending among=0.5 the OPD69 '.Light with the NA between 0.35 and 0.5 is drawn towards the intersection point of central ray and detection plane.These close NA correctly focus on detection system 25 less than about 0.35 light.Have light greater than 0.5 NA and be drawn towards position away from lens combination.The effect that redirects of light is that light is more concentrated in center intensity distribution and the external intensity distribution, thereby produces a zone broad and/or darker between two intensity distributions, thereby improves spatial filtering.
Though phase grid is set on the plate 50 or in the plate 50 in the embodiment shown in fig. 1, but phase grid also can be arranged on other the optical element or in other the optical element, for example collimation lens 14, beam splitter 13, if especially it is a cube beam splitter, perhaps objective system 18, and be preferably disposed on this moment on the surface of the lens of the system of radiation source 10.

Claims (7)

1. shaven head that is used to scan first optical record carrier and second optical record carrier, described first optical record carrier comprises first information layer and has first hyaline layer of first thickness, described second optical record carrier comprises second Information Level and second hyaline layer with second thickness different with described first thickness
Described shaven head comprises radiation source, is used to produce first radiation laser beam with first wavelength, and with second radiation laser beam with second wavelength different with first wavelength, described second radiation laser beam comprises center beamlet and outside beamlet,
An optical system is used to assemble first radiation laser beam and focuses on first information layer by first hyaline layer, and assembles second radiation laser beam and focus on second Information Level by second hyaline layer, and
A detection system is used to receive the radiation from first and second radiation laser beams of Information Level, and comprises the photosensitive region that is arranged in the detection plane,
Described optical system comprises the optical element with non-periodic phase structure, described phase structure comprises a plurality of concentric regions, be used for causing a wavefront skew that is offset near a flat wavefront on the whole at first radiation laser beam, and in the beamlet of center, cause the wavefront skew of the difference of the spherical aberration that a compensation causes owing to the different-thickness of first and second hyaline layers
It is characterized in that described optical element is transparent for the center beamlet and the outside beamlet of first radiation laser beam and second radiation laser beam, and
The wavefront skew that produces in second radiation laser beam is such, when the focus of central center light beam is positioned on second Information Level, the radiation of center beamlet and outside beamlet forms center intensity distribution and external intensity respectively and distributes in detection plane, described center intensity distributes and external intensity distributes by a dark in fact zone separately, and
Described photosensitive region is only caught the radiation that described center intensity distributes basically.
2. shaven head as claimed in claim 1 is characterized in that, described photosensitive region has the edge in the dark zone that is set at described intensity distributions.
3. shaven head as claimed in claim 1, it is characterized in that, described phase structure causes one on the whole near the skew of the wavefront of spherical aberration with defocus in second radiation laser beam, the described axial distance of change between the focus of the focus of center beamlet and outside beamlet that defocus.
4. shaven head as claimed in claim 1 is characterized in that, described phase structure is introduced in the beamlet of center and defocused.
5. shaven head as claimed in claim 1 is characterized in that, described phase structure is externally introduced in the beamlet and defocused.
6. shaven head as claimed in claim 1 is characterized in that, the axial distance between the focus of the focus of center beamlet and outside beamlet is 12.5 microns at least.
7. device that is used to scan two types optical record carrier, described device comprises a kind of be used to the scan shaven head of first optical record carrier and second optical record carrier and the information process unit that is used to carry out error correction, described first optical record carrier comprises first information layer and has first hyaline layer of first thickness, described second optical record carrier comprises second Information Level and second hyaline layer with second thickness different with described first thickness
Described shaven head comprises radiation source, is used to produce first radiation laser beam with first wavelength, and with second radiation laser beam with second wavelength different with first wavelength, described second radiation laser beam comprises center beamlet and outside beamlet,
An optical system, be used to assemble first radiation laser beam and focus on first information layer by first hyaline layer, and assemble second radiation laser beam and focus on second Information Level by second hyaline layer, and detection system, be used to receive radiation from first and second radiation laser beams of Information Level, and comprise the photosensitive region that is arranged in the detection plane
Described optical system comprises the optical element with non-periodic phase structure, described phase structure comprises a plurality of concentric regions, be used for causing a wavefront skew that is offset near a flat wavefront on the whole at first radiation laser beam, and in the beamlet of center, cause the wavefront skew of the difference of the spherical aberration that a compensation causes owing to the different-thickness of first and second hyaline layers
It is characterized in that described optical element is transparent for the center beamlet and the outside beamlet of first radiation laser beam and second radiation laser beam, and
The wavefront skew that produces in second radiation laser beam is such, when the focus of central center light beam is positioned on second Information Level, the radiation of center beamlet and outside beamlet forms center intensity distribution and external intensity respectively and distributes in detection plane, described center intensity distributes and external intensity distributes by a dark in fact zone separately, and
Described photosensitive region is only caught the radiation that described center intensity distributes basically.
CNB018061230A 2000-11-09 2001-10-30 Optical head for scanning record carrier Expired - Fee Related CN1213418C (en)

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CN1411598A (en) 2003-04-16
KR100805266B1 (en) 2008-02-20
US20020122377A1 (en) 2002-09-05
WO2002039440A1 (en) 2002-05-16
EP1340225A1 (en) 2003-09-03
JP2004513468A (en) 2004-04-30
JP4318916B2 (en) 2009-08-26
US6928043B2 (en) 2005-08-09

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